Most of the conventional positive displacement rotary pumps apply single stage pressurized flow to hydrostatically precompress the internal fluid volume to be displaced. The throttled pressure of a single staged flow contributes to the release of dissolved air into the internal pump volume to be displaced. The entrained air bubbles are imploded during the pump precompression and discharge cycles. Noisy operation and erosive wear are encountered.
To reduce the outgassing in the pressurized flow encountered in the precompression cycle, a series of constant and variable restrictions are located in the flow passage to alter the throttled pressure.
The application of the progressive staged flow for precompressing the internal pump volume to be displaced is described in typical vane, gerotor, and spur gear pumps. The invented precompressive staged flow feature is also applicable in other positive displacement rotary pump designs.